As anyone who has ever been pregnant, or has known a pregnant woman, knows quite well, pregnancy can put a great deal of stress on a woman's body. Not only does her weight increase--sometimes dramatically--but her center of gravity shifts. Further, her joints soften in preparation for delivering a baby. This is a recipe for joint pain, and knee pain is no exception.
Knee pain can be either significant or relatively insignificant--discomfort aside--during pregnancy. The difference depends upon whether the pain is the result of an injury, or is simply an effect of a woman's changing body. Women who experience pain in the knee after a fall, strain or injury should contact their physicians for an examination. Notes Dr. Raymond Poliakin in his book, "What You Didn't Think To Ask Your Obstetrician," a pregnant woman's soft joints make it more likely than usual that she will incur an injury during her pregnancy, particularly if she's active.
There are several potential types of knee pain during pregnancy. Knees can hurt because of injuries to the ligaments and soft tissue of the knee. This sort of pain is typically dull and aching, but may be sharp and stabbing if a woman moves in such a way as to exacerbate the injury. Women who stand or walk for a majority of the day may have aching legs, knees and feet simply because they're much heavier during pregnancy than they were before, which stresses joints and muscles, explain Heidi Murkoff and Sharon Mazel in their book, "What To Expect When You're Expecting."
Pregnant women also have a noticeable joint-softening effect during pregnancy, due to the hormone relaxin. This hormone, explains Dr. Poliakin, softens ligaments and relaxes joints so that a baby can pass through the pelvis during delivery. Softened joints are more flexible than normal, and women may inadvertently strain their knees and other weight-bearing joints when standing or stretching. Dr. Poliakin recommends particular care when stretching during pregnancy; though it maintains flexibility and is beneficial to the muscles, women should be aware of their limitations and not force joints beyond the point of comfort.
As much as exercise benefits both a pregnant woman and her baby, higher-impact forms of exercise may result in joint injuries. Running, in particular, may contribute to knee pain in pregnant women. In their book "You: Having A Baby," Drs. Michael Roizen and Mehmet Oz explain that relaxin-loosened joints can't absorb impact as well as normal joints, since the joints are slightly floppy and bones move against one another. While some women run comfortably throughout pregnancy, those who find that they're experiencing knee pain after running may wish to look for other, lower-impact forms of exercise.
Unfortunately, unless knee pain is the result of an injury and needs medical treatment, there's little that pregnant women can do to treat the pain. Sore knees as a result of increased body weight will resolve themselves once the baby is born. In the interim, Drs. Roizen and Oz recommend hot or cold packs for uncomfortable, sore joints. While pregnant women should always consult their physicians before using over-the-counter medications, most obstetricians allow acetaminophen for analgesia during pregnancy.